A California day trader and three pals thought they had dreamed up the perfect easy money scam.

For three years, these two-faced traders duped Wall Street bankers into thinking they were big-time institutional investors — thereby unlocking a door to a treasure trove of nonpublic information on 15 biotech deals, according to Department of Justice allegations.

Although the traders had promised — as a matter of everyday business on Wall Street — not to trade on the insider dope, they did and pocketed $3.2 million in fraudulent profits before they were busted, prosecutors charged on Wednesday.

Steven Fishoff, 58, his brother-in-law and two friends were charged with securities fraud and conspiracy after being arrested by FBI agents at their respective homes in California, New Jersey and Florida.

“They allegedly rigged the game so they would always win, and their profits came at the expense of legitimate investors, who were not privy to this inside information,” Paul J. Fishman, the US attorney in New Jersey, said in a statement.

The unwitting but red-faced unidentified bankers aren’t accused of any wrongdoing.

The insider info entirely involved upcoming secondary stock offerings, news that, once made public, would likely drive down the price of the company’s stock. The traders, acting on that likelihood, shorted the stocks in advance of the offerings, it is alleged.